Dust counter



July 3o, 1940.

F. B. RowLEY 2,209,614

DUST COUNTER Filed May 28,

'ai Y INVENTOR FRAN? B. ROWLEY iPaq/fl ATTORNEYS F. B. ROWLEY July 30,1940.

DUST COUNTER 2 t e e h s S .Tv e e .n s 2 y Ov l w y m Pn .m 2 5 1 2 n um. :Tm 1J\ 4 rNvEN-roR 45 FRA B. no L Ev BY Lul fo-u l ATTOH NE YSPatented July 30, 1940 UNITED STATES PATENT OFFICE 5 Claims.

This invention relates to new and useful improvements in dust countersor apparatus for measuring or ascertaining the number of dust particlesin a given volume of air.

All atmospheric or free air contains dust, and the dust concentrationthereof may vary considerably in different localities. Because air isessential to life, it is of utmost importance that some means beprovided whereby the dust concentration of air may be substantiallyaccurately determined, so that it may be definitely known whether or notthe air in any given space or room is injurious to health, or createsother hazards. In some industrial plants, the dust concentration may berelatively high, thereby creating a very dangerous situation from ahealth standpoint. It is not a simple matter to accurately measure orascertain the dust concentration of a given volume of air, primarilybecause of the infinite number of invisible dust particles which areoften contained in the air, and which are extremely diflicult toseparate from the air and evaluate.

The possible hazards oi dusts depend upon their chemical and physicalcharacteristics, and their concentrations in the air. Manyinvestigations have been made by technical institutions vand others, todetermine the condition or purity of the air in numerous industrialplants, and the results of such investigations have definitely shownthat the air in some plants is exceedingly detrimental to health,because of the relatively high dust concentration thereof. It is,therefore, of utmost importance that some means be provided whereby thecondition of the air in a given space or room may conveniently beperiodically checked, thereby to ascertain the dust concentrationthereof.

In spite of the fact that a large amount of investigational Work hasbeen done concerning the amount of dust in the air, to the best of myknowledge, no practical method has, as yet been devised and accepted formeasuring the amount of dust in various samples of air or for rating thequality of air in regard to its dust content. 'I'he dust particles inthe air are extremely line, the greater majority of them not beingvisible without the aid of a microscope. The concentrations of particlesof dust runs from a few thousand to many millions of particles percubic-foot of air. In order to know whether or not, any dust constitutesa physical or other hazard, it is desirable to have as a part of theinformation, its concentration, or the numbers of particles contained ina given lvolume of air, their approximate (Cl. 'Z3-51) size, and thevphysical characteristics thereof. This information `cannot be 'obtainedby any simple visual method, such as that often used a for determiningthe relative density of smoke or fumes in the air. In such cases, astream of smoke or fumes may be projected against -a relatively roughsurface orl paper which will collect a sample that may be compared incolor, density of path, or other visible characteristics, to a standardsample, thus giving a qualitative analysis only. Such-methods may beadapted to a comparative rating for the density of fumes or smoke, butit is impossible to use them to measure the amount of dust in the airwhich we breathe. 15

Even though there are large numbers of dust particles per cubic foot inthe average air, samples of this air drawn through any of the well-knownsmoke or fume recording devices now in use, would show absolutelynothing as to the number of dust particles for a given volume of air. Byany of the methods now used for rating thedensity of fumes or smokedrawn into the apparatus, lit would be impossible to get any accurateresults whatsoever by the use of a microscope,.due rst to the fact thatthe particles yWould not be effectively collected, and secondly, thesurfaces used for collecting the dust in such apparatus are so rough anduneven that the particles collected could not vbe focused in the fieldof the microscope. Such smoke recording devices are of an entirelydifferent class than the instruments used to count dust particles in theair, and, should vnot be confused with them. With smoke and fumes,` itis not `necessary to count the actual particles. The density is so greatthat al partial collection and rough visual comparison is usuallysuicient. Dust particles suspendedin air are very fine, and, as comparedwith smoke and fumes, are very much more scattered in the air andimpossible to detect by any of the ordinary visual methods.

Because the dust particles are so minute or innitestimal, and further,because they are so widely scatteredl in the air, the problem ofaccurately measuring or ascertaining the dust concentration of a givenvolume of air, becomes far more diliicult, and requires the use of ahighly sensitive instrument, which should be so constructed that in thedust sample or record collected thereby, the dust particles are sodeposited on the record plate, that they may readily be accuratelycounted, `when the plate is placed under a high-powered microscope. Theactual dust count method makes it necessary to deal with Si A' dust invery small quantities of the air. For instance, in many cases, it isimpossible to actually count the particles in more than a fraction of acubic inch of air.

While no single method of measuring dust in the air has yet beenaccepted as a standard, several dust counting methods have been devisedand used with some success. In general, these methods may be dividedinto two classes: rst, that in which the dust is washed out of a largequantity of air, and an actual count made with a microscope on a smallfraction of the washing liquid, thus giving a dust count which, bycalculation, may be used to show the count in yany definite volume ofthe original air taken into the sampling device; and secondly, a methodin which the dust particlesy are separated from the air by impinging astream of the dust laden air onto a smooth, sticky surface which willretain the dust particles in a concentrated mass, and whereby thecollected dust particles may be placed under a microscope and counted.

In the first method, above mentioned, a comparatively large volume ofair is passed through a water or other liquid washer, which retains alarge percentage of the dust particles. A sample of the liquid is thendiluted and placed under a microscope and a dust count taken of thatpart which falls within the field of the microscope, which is only asmall fraction of the water used. From this count, the dust in theoriginal air is calculated. In the second method, the dust particles arecollected on a small area of the surface of a record plate, whereby thedust particles are, in eiect heaped one on top of another. This dustsample is then placed under a microscope and the particles of the masscounted I have found, from actual experience, that in many cases, it isimpractical or even impossible to use the washing method, due to thetime involved or the kind of dust in the air. In the washing method,relatively large volumes of air must be drawn through the Washer, thustaking a considerable period of time for gathering the sample and, inaddition to this, a final sample must be prepared in the laboratory, andthe dust allowed to settle out of the prepared sample for a periodvarying from 15 to 30 minutes, before the count can be taken. Thismethod is therefore not well adapted for field work, where it is highlydesirable that a method be employed which permits samples to be quicklytaken at any time, and whereby the dust particles of the sample may bereadily and quickly counted to immediately measure or ascertain the dustconcentration of the air in any room or space. There are many kinds ofdust such, for example, as oily carbon, which cannot be taken out bywashing, and therefore their concentration in the air cannot bedetermined by the washing method.

I have also found by experience that it is impossible, in most cases, tomake an accurate determination of the amount of dust in the air by anyof the viscous plate type of counters thus far developed. There are atleast two important elements lacking in each of them, with which I amfamiliar. In the air operated or suction type, air is usually drawn inby the stroke of a pump, or similar method, and the dust from thecomplete volume of the sample is deposited in a single spo-t on thesampling plate. By this method, the velocity of impingement of the airagainst the sampling plate varies from zero to maximum, and then down tozero through the sampling stroke of the pump. A uniform percentage ofdust cannot be taken from the air by such varying air velocities, andtherefore such samples cannot be relied upon as giving representativedust counts. The concentration of dust in many samples of air is not sogreat that the sample must be confined to a fraction of a cubic inch, ifall of the dust particles are to be collected in a single spot andcounted under a microscope. It is impossible with any of the methods nowinv use to get air samples of such small volume which will` depositVrepresentative samples of the dust in the air.

It is therefore, highly desirable that a novel method and apparatus beprovided, whereby the dust particles of a given volume of air may becollected and so disposed or arranged upon a suitable surface, thatwhen. placed under a microscope, all of the particles contained in thecollected sample, may readily and conveniently be counted, whereby theconcentration of dust in the air in any given space or room may readilyand quickly be accurately measured to determine the condition of theair.

An important object of the present invention, therefore, is to providelan apparatus, whereby the dust concentration of air may be accuratelymeasured or ascertained, and which does not require the services of askilled mechanic or technician to operate it.

A further object of the invention resides in the provision of a dustcounter comprising a plate having a suitable surface for receiving asample of dust, and which counter is so constructed that the dust isdeposited upon said plate in an elongated sample of uniform density, andin which the dust particles are so disposed that they may readily becounted, when placed under a microscope,

A further object is to provide an apparatus for measuring or determiningthe number of dust particles contained in a given volume of air, whichcomprises a plate having a viscous coated surface, and a mechanism forimpinging a stream of dust laden air against the surface of said plateat a uniform velocity and simultaneously moving the plate at apredetermined speed with respect to the velocity of the air stream, thespeed of the plate being regulated to suit the concentration of dust in.the air, and whereby the dust particles contained in the air stream aredeposited upon the surface of the plate in an elongated pattern ofuniform density, whereby the dust particles may readily be accuratelycounted, when placed under a highpowered microscope.

A further and more specific object of the invention is to provide anapparatus of the class described, comprising a dust separation chamberhaving a plate movably mounted therein, and a wall of said chamber beingprovided with a small orifice through which dust laden air may be drawninto the chamber, and means being provided for drawing air through saidorifice into the chamber at a uniform rate of flow and simultaneouslymoving the plate beneath or past the orice, whereby the dust particlescontained in the air are deposited on the surface of the plate in anelongated pattern of uniform dust density, whereby the dust content of agiven volume of air may readily be measured or counted to accuratelydetermine the dust concentration of the air in a given room or space.

Other objects of the invention reside in the novel construction of theapparatus, which is provided with suitable adjustments for adapting itto meet all conditions', where such an apparatus may be used; in theprovision of means whereby the density of the dust particles collectedon the record plate maybe relatively varied for any given volume of air,thereby to facilitate the counting of the dust particles contained inthe sample; and, in the provision' of a dust counter comprising acylinder having a. dust separation chamber communicating with one endthereof and provided with a suitable air intake orice, and said chamberhaving a record plate movably supported therein and adapted to receive adust sample, and means being provided for maintaining a constant vacuumin said chamber and simultaneously moving the record plate beneath orpast the orice, whereby dust particles drawn into the chamber throughsaid orice will be deposited upon the surface of said plate in anelongated pattern of uniform density; and, in the simple and inexpensiveconstruction of the apparatus, which is compact and convenient tooperate and readily lends itself for manufacture in quantity production'at 'small cost.

Other objects of the invention will appear from the followingdescription and accompanying drawings and will be pointed out in theannexed claims.

In the accompanying drawings, there has been disclosed a structuredesigned to carry 'out the various objects of the invention, but it isto be understood that the invention is not confined to the exactfeatures shown as various changes may be made within the scope of theclaims which follow. n

In the drawings:

Figure 1 is a side elevation of an apparatus designed to carry out myinvention;v

Figure 2 is a plan view of Figure 1; Y

Figure 3 is a sectional elevationon the line 3--3 of Figure 1;

Figure 4 is an enlarged detail sectional elevation on the line 4-4 ofFigure 3; I

Figure 5 is an end view o-f the apparatus, with the cover removed fromthe chamber to illustrate the record plate supported therein;

Figure 6 is a detail sectional view on the line 6 6 of Figure 5; and lFigure 7 is a perspective view of the record plate removed from thechamber 'and showing a dust sample deposited thereon. i 'Y In theselected embodiment of the invention here shown, there is illustrated inFigures l and 2, for purposes of disclosure, an apparatus comprising acylinder, generally indicated by the numeral 2, and having a casing 3 atone end whose walls define a vacuum or dust separation chamber 4. Theend wall 5 of the' casing 3 is removably supported by suitable screws 1,and is provided with a small orice 8 through which air may be drawn intothe chamberd.

A head 9 is suitably secured to the opposite end of the cylinder 2 andguidin'gl'y supports a piston rod Il provided at its projecting end witha suitable hand grip I2. A piston I3, of conventional construction, issecured to the opposite end of the piston rod II, and is operativewithin the cylinder by manipulation of the piston rod I I. A suitablepassage I4 establishes communication between the interior of*l thecylinder 2 and the dust separation chamber 4, asbest illustrated inFigure 4.

The cover 5 is secured to" the side walls I5 and bottom wall I6 inhermetically Ysealed relation. The upper wall I1 of the chamber 4 isremovably supported by such means as a yoke I8, pivoted at 2| to theside walls I5 and having a suitable screw 22 received in threadedengagement therewith, whose terminal 23 is adapted to engage thetop'wall I1 to retain it in closed position, as shown in Figures 4 and5. A suitable packing or gasket 24 is interposed between the top wall Il and the adjacent ends of the walls of the housing 3, to provide an airtight joint therebetween. The top wall I'I is shown having its endssuitably notched, as indicated at 25, to retain it in position withrespect to the yoke I8.

A suitable record plate, generally indicated by the numeral 26, ismovably supported within the chamber 3, and is adapted to pass beneathor past the orifice 8, when the apparatus is operated, as willsubsequently be described. One side of the record plate 26 is coveredwith a suitable viscous or sticky material to provide a surface adaptedto receive the dust particles, and to which said particles will adhereso that the plate may be conveniently removed and placed under amicroscope for counting the dust particles. v

An important feature of the present invention resides in the novelmanner of depositing the dust particles upon the surface of the recordplate 26, whereby they are disposed in an elongated pattern, asindicated at 21 in Figure 7, extending crosswise of the plate, andwhereby the dust pattern or sampleon the plate will be of uniform dustdensity, so that the particles thereof may readily be counted.

To thus collect and depositthe dust particles of a given volume of airupoii the surface of the plate 26, the plate is supported in a suitableholder 28, having a clip 29 at one end for engaging the end of the plate26, and provided at its opposite end with a suitable retaining spring3l, secured at 32 to the holder 28 and having its free end 33 providedwith spaced prongs 34 between which one end of the plate is received, asclearly illustrated in Figures 4 and 5. The spring 3I removably supportsthe plate 26 in the holder 28, whereby it may readily be removedtherefrom, as will subsequently be described.

The holder 28 is mounted for longitudinal sliding movement in a suitablecarriage 35 supported within the vchamber and having oney end oranelongated tubular member or hub 36 secured in a bore 3T providedtherein, as best illustrated in Figure 6. The tubular member 36 isslidingly received in a suitable packing boX 38, provided in one vof theside walls I5 of the casing 3, vas best illustrated in Figure 6. A shaft39 is shown rotatably supported in the member 36 .and is provided at itsinner end with a small pinion 4I which meshes with a rack 42 provided onthe adjacent side of the holder 28. The rack 42 is slidable in alongitudinal groove 43 provided in the carriage 35. A suitable nger grip44 is secured to the outer end of the shaft 38, whereby the shaft may beyconveniently rotated to longitudinally translate the vho1der28 in thecarriage 35, when it is desired vto remove the record plate 26 from thechamber 4. A space 45 is provided between the bottom of the carin a plug49 received in threaded engagement with a wall l5, shown at the righthand side of Figures and 6. The spring 46 constantly urges the carriageinto the position shown in Figures 5 and 6, wherein the record plate 26is out of registration with the intake orifice 8, as best illustrated inFigure 6.

Means is provided for moving the carriage 35 from the full to the dottedline position, shown in Figure 5, during the operating stroke of theapparatus, and' at a predetermined speed with respect to the velocity ofthe air drawn into the chamber 4 through the orice 8.

In Figures 1 and 2, I have shown a mechanism for simultaneouslyoperating the carriage 35, when air is drawn into the chamber 4 todeposit a dust sample on the surface of the plate 26. The mechanismherein disclosed, is shown comprising a lever, generally indicated bythe numeral 5|, having one end arranged to engage the terminal orknurled head 44 of the shaft 39. The opposite end of the lever 5| has apin 52, which is mounted in a member 53, shown pivoted to the lever 5Iby a suitable pivot 54. The end portion 55 of the member 53 engages alimit stop 56, carried by the lever 5|, and against which it is normallyheld by a suitable spring 51. By this arrangement, the pin 52 isyieldably connected to the lever 5|, so that should the carriagev reachthe limit of its movement against the tension of the spring 46', beforethe piston rod has been moved to the limit of its outward movement, nodamage will be done to the parts. 1 A suitable cam bar 58 is shownadjustably secured to a rod 59, mounted for sliding movement in asuitable guide 6| secured to the cylinder 2. A connecting member 62 issecured to one end of the rod. 59 and to the piston rod whereby the rod59 is movable asl a unit with the piston rod |I. The cam bar 58 is shownprovided with a suitable segment member 63, slidingly supported in aguide 64 and adapted to be secured against movement in said guide by asuitable clamping or adjusting screw 65, illustrated in Figures l and 2.By loosening the screw 65, the cam bar 5B may be relatively adjustedabout the supporting pivot 66 to vary the angle of the cam edge 61thereof, with respect to the axis of the piston rod II. The pin 52 isadapted to engage the edge 61 of the cam bar 58, when the piston rod ispulled outwardly, as will readily be' understood by reference to Figure2. A suitable vacuum gauge, generally indicated by the numeral 68 issecured to the back wall 46 of the casing 3 and is in directcommunication with the dust separation chamber 4.

In the operation of the novel apparatus herei-n disclosed, the plate 26is secured in position on the holder 28, and the top wall I1 of thechamber 4 is then secured in position by manipulation of the clampingscrew 22. The apparatus is the-n preferably supported in substantiallythe position shown in Figure l, and the piston drawn outwardly at acertain rate of speed, determined by the vacuum to be maintained in thechamber 4. The gauge 68 will register the vacuum in the chamber 4, andis so positioned that the operator may readily see it while operatingthe piston rod II. By maintaining a predetermined vacuum in the chamber4, during the suction stroke of the piston rod air is drawn into thechamber through the orice 8 at a uniform rate of ow, which is of utmostimportance in order to obtain a true dust sample.

The air thus drawn into the chamber through the orifice 8, impingesagainst the viscous-coated surface of the record plate 26, whereby thedust contained in said air is deposited on the surface of the plate inan elongated pattern of substantially uniform dust density, as indicatedatv21 in Figure '1.

The operating mechanism for the carriage 35 is so adjusted that the endportion 69 of the lever 5| will begin to move the tubular member 36inwardly immediately following the initial movement of the piston I3,whereby the operator may move the piston at a rate of speed to maintaina constant vacuum in the chamber 4 during the full operating stroke ofthe apparatus, or until the plate 26 has passed beneath the orice 8,from the full to the dotted line position, indicated at 10 in Figure 5.

The lever 5| is supported on a fixed pivot 1|, suitably secured to thecylinder and is actuated by the edge 61 of the cam bar 68 engaging thepin 52, when the piston rod I I is pulled outwardly, as will readily beunderstood by reference to Figure 2. The tension of the spring 51 issuch as to overcome friction of the parts and the tension of spring 46'so that, in normal operatic-n, member 53 will not pivot relative tolever 5|. The cam edge 61 of the cam bar 58 is so shaped that themovement imparted to the carriage 35 will be uniform the full length ofits travel, and whereby it bears a definite relation to the travelingmovement of the piston I3. By varying the angle of the cam edge 61, thespeed of travel of the carriage with respect to the movement of thepiston |3 may be varied to suit the concentration of dust in the air.

When the apparatus has been operated to deposit a sample of dust uponthe surface of the plate 26, the clamping screw 22 is unscrewed orloosened, to permit the upper wall I1 to bev move the plate 26, theknurled head 44 of the shaft 39 is rotated in one direction, whereby oneend of the holder 28 may be projected from the upper open end of thecasing, so that the operator may readily grasp the holder with his ngersand remove it bodily from the carriage, if he so desires. The recordplate 26 is then removed from the holder and placed under a powerfulmicroscope, whereby the dust particles deposited on the surface thereofmay readily and conveniently be counted.

A suitable post 12 is secured in fixed relation with respect to thecylinder 2, and cooperates with the lower wall I6 of the casing 3 tosupport the apparatus in the position shown in Figure l. A suitablecushion spring 13 may be mounted4 on the piston rod I I, within thecylinder, and has one end engaging the head 9 and. its opposite endadapted to be engaged by the piston I3, thereby to' cushion the outwardmovement of the piston.

, By depositing the dust particles in an elongated pattern upon thesurface of the record plate 26, as sho-wn at 21 in Figure '1, thecollected dust particles on the surface of the plate 26. whichrep-resent the dust content of a given volume of air, may readily becounted, as hereinbefore stated. If the air is heavily laden with dust,the operating mechanism of the carriage may be operated to travel at aslightly higher rate of speed, with respect to the vacuum maintained inthe dust separation chamber, in order that the particles collected onthe record plate will be spread over a relatively greater surface,thereby to facilitate counting them. If the dust content of the air isvery light, it may be desirable to adjust the cam bar in such a manneras to retard the movement of the carriage, thereby causing the clustparticles collected from a given volume of air to be deposited in a moreconcentrated form on the record plate. The adjustability of the cam bar58 thus makes it possible to control the depositing of the dustparticles upon the surface of the record plate, whereby the pattern ofdust particles collected from a given volume of air may be varied tosuit the concentration of dust in the air, and to facilitate counting.

In the accompanying drawings I have shown, and in the specificationdescribed in detail, a simple, but practical apparatus embodying myinvention. It is to be understood, however, that the specific disclosureis for the purpose of exemplication only, and that the scope of theinvention is dened in the following claims, in which I have endeavoredto distinguish it from the prior art so far as known to me.

I claiml as my invention:

l. In a. dustcounter, a dust separation chamber having an orice in awall thereof, a suction device for drawing atmospheric air through saidoriiice into the chamber at a uniform velocity, a holder within thechamber, a record plate removably supported on the holder and having asurface for receiving dust particles drawn into the chamber through saidorifice, and means for moving' the holder to impart lateral uniformmovement to the plate, whereby a transverse area thereof is exposed tothe orice to receive dust particles drawn into the chamber through saidoriiice, and whereby an elongaxted dust record of uniform density, isdeposited on the plate. i

2. In a dust counter, a dust separation chamber having an air intakeorice, a suction pump connected to the chamber, a plate removablysupported in the chamber and having a surface for receiving dustparticles, means operated by the pump, for simultaneously moving saidplate at a predetermined uniform speed with respect to a given vacuum inthe chamber, and means for varying the timing between the suction of thepump and the movement of the plate,

whereby the apparatus is adapted for taking dust samples of air ofdiiferent dust concentrations.

3. In a dust counter, a cylinder havinga casing at one end whose wallsdenne a dust separation chamber, means establishing communicationbetween the cylinder and chamber, a wall of the casing having an airintake orifice, a plate movably supported in the chamber, a pistonoperatively mounted in the cylinder and whereby dust laden air may bedrawn into the chamber through said orice, and a mechanism operativelyassociated with the piston and adapted to move said plate beneath saidorifice at a predetermined uniform speed, whereby dust particles drawnthrough said orice are deposited on the surface of said plate in anelongated pattern of uniform density, and whereby the dust particles onsaid platemay readily be counted, when the plate is placed under amicroscope, thereby to determine the dust content of the air in a givenspace or room.

4. In a dust counter, a dust separation chamvice connected to the.chamber, a record plate removab-ly supported in the chamber and having asurface for receiving dust particles, means operated by actuation of thesuction device for simultaneously moving said plate at a predetermineduniform speed with respect to a given vacuum in the chamber, and meansfor varying the travel of the record plate with respect to the vacuum inthe chamber, whereby the apparatus is adapted for taking dust samples ofdifferent dust concentrations.

5. In a dust counter a dust separation `chamber, a member having anorifice opening into said separation chamber for the introductiontherein of gas carrying dust particles from without the chamber, asuction device for drawing gascarrying dust into the chamber throughsaid oriiice at uniform velocity, a holder member for holding a recordplate in juxtaposition to the orice containing member for the deposit onthe record plate of dust entering through the orice, a carriage movablein a xed limited path and supporting one of the juxtaposed members formovement relative to the other of said members whereby dust entering theorifice will be deposited in a path across the record plate determinedby the movement of the carriage.

FRANK B. ROWLEY.

lber having an air intake orice, a suction de-

